For this one, you need to defeat the Final Boss without skipping, there's no real advice i can give to you about how to beat him, as it requires a lot of trial and error to learn his moves, when you beat one of the boss' phases, you'll get a checkpoint to the next one, the only one you need to worry about is the last phase which will take you a good while to beat, it's been a long time, so i can't really give a lot of advice, but i can put a video, if it helps.
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